The average depth of the ocean is 2.3 miles (3.7 km), but some parts of the world’s seas are much deeper.
Scientists measure the ocean’s depth using sound waves, which are sent out by a ship and return to the surface with pulses of energy.
This technique has been used to pinpoint many of the world’s deepest points – including Challenger Deep in the Mariana Trench near Guam.
The Challenger Deep
The deepest point in the ocean is called the Challenger Deep, found in the Mariana Trench southwest of Guam. It lies 35,814 feet below sea level.
The Challenger Deep is named after the HMS Challenger, an expedition ship that made the first measurements of depths using a weighted rope in 1875. The expedition circumnavigated the world and laid the foundations for modern oceanography.
It has been measured many times, by various methods, including single and multibeam sonars and unmanned submarines. The most recent measurement, by the United States Center for Coastal & Ocean Mapping, was in 2010 at 10,994 meters (35,994 feet), with an error of +- 40 meters.
In 2012, filmmaker James Cameron became the first human to reach the Challenger Deep, in a submarine designed by himself. He spent three hours there, but the pressure took a toll on his equipment: batteries died, sonar failed and some of his thrusters malfunctioned.
The Mariana Trench
The deepest point on Earth is the Mariana Trench, a crescent-shaped hole in the ocean. It’s 2,550 kilometers long and 69 kilometers wide, and it plunges to the bottom of the world’s oceans.
The trench was created by a process called ocean-to-ocean subduction. During this event, two massive slabs of oceanic crust, known as tectonic plates, collide. The two slabs then bend beneath each other, creating a deep hole at the intersection of their sinking edges.
In the Mariana Trench, life thrives in extreme conditions. Some animals live in complete darkness and face water pressure so high it would crush the body of a human being.
Animals like crustaceans with aluminum shields, blind, translucent snailfish, and a deadly predator called the sea pig thrive in this harsh environment. Yet surprisingly, this area is home to many cool creatures that were discovered by scientists on expeditions.
The Pacific Ocean
The Pacific Ocean is by far the largest of the world’s oceans, covering nearly 30% of the Earth’s surface. Its size is double that of the Atlantic and more than two times that of the Indian Ocean.
It is the home of a unique biodiversity, with kelp beds and coral reefs found in all but the polar regions of the Earth. Its currents also allow for mixing of marine life coming from other parts of the planet.
In the eastern part of the Pacific, there is a well-defined main current (called the North Equatorial Current) which runs westward along latitude 15degN. A few branches also emerge and flow toward both north and south. These are known as the Kuroshio and counter equatorial currents, respectively.
The Atlantic Ocean
The Atlantic Ocean is the second-largest of the world’s ocean basins. It is also the second youngest of the five major oceans, having formed during the Jurassic Period about 150 million years ago after the breakup of the supercontinent Pangaea.
It extends from the Arctic Ocean, northward to Antarctica. It is divided into two basins, the North Atlantic and South Atlantic, by the Equator.
At its deepest point, the Atlantic Ocean is dominated by a submarine mountain range called the Mid-Atlantic Ridge that extends from Iceland in the north to 58 deg south latitude. This ridge is constantly being created in the region by magma rising from under the earth’s surface.
A great rift valley extends along this ridge. The rift pushes the Americas and Europe away from each other, widening the ocean floor at an average rate of about 0.4 inch (1.5 cm) per year. The Mid-Atlantic Ridge is also the source of numerous seamount
.